1. Field of the Invention
The present invention relates to oceanographic measuring systems, and more particularly to surface current mapping systems.
2. Description of the Prior Art
A radar using vertically polarized radiation can observe backscatter from the sea surface to infer surface currents for such applications as coastal research and pollution monitoring. One such prior art system is shown in U.S. Pat. No. 4,172,255 to Barrick et al. Backscatter from advancing and receding waves with a wavelength half that of the radar wavelength gives signals allowing the measurement of ocean currents along the line of sight. One limitation of these Doppler radar systems to date has been the inability of directly measuring the transverse component of the current without a second radar located a considerable distance from the first, so that a given patch of ocean is observed from two radars with nearly orthogonal viewing directions. This introduces some limitations on the siting of these radars and a degree of complication because the maintenance of two radar sites and the need to transmit data from one radar to the other to generate real-time current maps.
Another factor is that with two radars, there is sometimes an incomplete spatial overlap between the two radar volumes needed to measure the full current vector, which may lead to errors in complex flows. However, here it will be shown that the transverse component of the current can be measured using correlation analysis of the received signal from spatially separated receiving antennas with a single radar. This technique has been used for atmospheric radars and for optical remote sensing applications.
There are numerous applications fgr monitoring surface currents near shore (out to 30 km). The recent oil spill at Prince William Sound (Exxon-Valdez) provides a dramatic example of a case where an accurate current map could have significantly improved the damage control. Other applications include mapping the current field around ports or fish spawning grounds and as an oceanographic research tool.